1. Field of Invention
This invention relates to radioactively tagged erythrocytes and to a process for their preparation. The invention also relates to agents which contain these tagged erythrocytes and which are suitable for scintigraphic display, and to a process for producing these agents.
2. Description of Prior Art
The determination of erythrocyte volume, of erythrocyte survival time, and the detection of an enteral blood loss as well as scintigraphically displaying the blood pool and spleen are routine methods in nuclear medicine which are carried out with radioactively tagged erythrocytes. Methods of this kind are described, for example "Haematologie" by H. Heimpel and in Nuklearmedizinische Funktionsdiagnostik by D. Emrich, George Thieme Verlag, Stuttgart 1971. In methods of this kind, there has to be, on the one hand, a stable bond between the radioactive isotope and the erythrocytes. On the other hand the isotope used has to have suitable physical properties, above all in regard both to the energy of the gamma rays emitted and to half life. It is already known that 51.sub.Cr can be used for tagging erythrocytes. Corresponding methods are described, for example, by Gray, S and K Sterlin in "The tagging of red cells and plasma proteins with radioactive chromium" by J. clin. Invest. 29, 1604 (1950). In the 51.sub.Cr used for this purpose, the bond between isotope and erythrocytes is very strong. Unfortunately, this isotope gives off a high level of radiation during investigation on account of its long half life of 27.8 days. Attempts have already been made to tag erythrocytes with the 99m.sub.Tc readily available through generators, cf. for example Bull, U., K. W. Frey, H. Langhammer, K. J. Pfeiffer and N. Napp: "Zur Problematik und Methodk der Milzszintigraphie und 99m.sub.Tc -markierten, warmealterierten Erythrocyten" Fortschr. Rontgenstr. 117, 1 (1972) 86. In this radionuclide, however, the strength of the bond with the erythrocytes is very weak and cannot be compared with that of 51.sub.Cr. Accordingly, tagging with 99m.sub.Tc has only been carried out on a limited scale in the past.
Accordingly, the object of the invention is to obviate the disadvantages referred to above and, in particular, to provide an agent for functional diagnosis in nuclear medicine in which there is a bond of high strength between the radionuclide and the erythrocyte. This object is substantially achieved by the invention.